The present invention relates to a three-dimensional shape and color detecting apparatus employed, for example, in a three-dimensional scanner, capable of detecting a three-dimensional shape of an object and the color thereof. Conventionally, three-dimensional shape and color detecting apparatuses for detecting a three-dimensional shape of an object and the color thereof based on light reflected by the object have been known.
An example of such apparatuses is disclosed in Japanese Patent Provisional Publication P2001-145126A (published on May 25, 2001). In this publication, the apparatus includes a laser unit which sequentially emits red, green and blue laser beams toward an object, and receives the reflected beams with a CCD (Charge Coupled Device). Then, based on an image formed on the CCD, distances to various portions on the object are obtained, thereby detecting the three-dimensional shape of the object. Further, in this apparatus, for each of the three color beams, the reflected components are received with the CCD, and detects the color of the object.
Another known method is where a point light source (such as flash light emitted by a strobe device) is used to illuminate an object and the color thereof is determined. When a light source is located at a predetermined fixed position, however, it is difficult to detects the color of the entire object, as described below.
FIG. 14 schematically shows a structure of the conventional shape detecting apparatus. In the structure shown in FIG. 14, a point light source P30 and a CCD camera P11 are arranged on the left-hand side (which will also be referred to a front side of the object) of an object P3 to be detected. A ray RB of light emitted by the point light source P30 and incident on a point B at a side surface of the object P3 has a relatively large incident angle (i.e., an angle β formed between the ray RB and a normal NLA to the surface of the object at a point where the ray strikes the object P3) in comparison with the incident angle α of the ray RA striking a point A located at the front side of the object P3. DB1 and DB2 denote intensity distributions of reflection components at the points A and B, respectively.
Therefore, the quantity of light of reflection components of the light from the points A and B incident on the CCD camera P11 are considerably different. In particular, the quantity of light of the component from the point B to the CCD camera is very small, and a color of the object at the point B cannot be detected accurately.
There is another method, in which the color and shape of the object are measured at various angles, and then based on the obtained measurement data, the shape and color of the object is determined. In this method, however, stepwise color variation which does not exist in reality may appear in the entire three-dimensional image obtained in accordance with the above method. This problem will be additionally described in detail below.
First, when the entire three-dimensional image of the object P3 is generated, as shown in FIG. 15A, the three-dimensional shape and color of the object P3 are detected from its front side. With this condition, an area AR1 is measured. Then, as shown in FIG. 15B, the object P3 is rotated by 90 degrees, and the three-dimensional shape and color are detected from the left side of the object. Then, an area AR2 is measured. Similarly, the detection is performed from the rear side and the right side of the object with rotating the object P3 by 180 degrees and 270 degrees, respectively. Then, the images thus obtained are synthesized to form a final image of the object P3 as shown in FIG. 16.
In the three-dimensional shape of the object P3 shown in FIG. 16, a left-hand side portion SLH of a line C represents an image when the object P3 is oriented as shown in FIG. 15A, and a right-hand side portion SRH of the line C represents an image when the object P3 is oriented as shown in FIG. 15B.
As previously mentioned, in the conventional three-dimensional shape and color detecting apparatus, the color of a surface which faces aside the light source cannot be detected correctly. Therefore, when the object P3 is oriented as shown in FIG. 15A, the color of a portion in the vicinity of the line C cannot be detected correctly. Since the image of the left-hand side portion of the line C is detected when the object P3 is oriented as shown in FIG. 15A, the color CLH of this portion of the finally obtained three-dimensional image (shown in FIG. 16) is different from the true color of this portion of the object P3.
On the other hand, the color CRH of the right-hand side area of the line C is detected when the object P3 is oriented as shown in FIG. 15B. Therefore, it is expected that the color of the image of this portion of the three-dimensional image correctly represents the true color of this portion of the object P3.
As above, there is a step of color difference at the border line C.